1. Field of the Invention
The present invention relates to elastic wave devices in which an IDT electrode and a high acoustic velocity film are stacked on a LiNbO3 substrate, and more particularly to an elastic wave device that utilizes a leaky elastic wave.
2. Description of the Related Art
Elastic wave devices, which are used as filters of communication devices or the like, are desired to achieve high frequency and low loss. Japanese Unexamined Patent Application Publication No. 2008-177885 discloses a surface acoustic wave filter that uses a 64°±3° Y-X LiNbO3 substrate or uses 41°±3° Y-X LiNbO3. In Japanese Unexamined Patent Application Publication No. 2008-177885, IDT electrodes are disposed on a piezoelectric substrate composed of LiNbO3. In addition, a protection film composed of SiO2, SiNx, Si, or Al2O3 is disposed at a surface-acoustic-wave-propagating portion of the LiNbO3 substrate. In Japanese Unexamined Patent Application Publication No. 2008-177885, each reflector electrode includes a busbar electrode substantially at the center in the extending direction of electrode fingers. The busbar electrode extends in the propagation direction of the surface acoustic wave and has a width that is less than or equal to half the wavelength of the surface acoustic wave. This configuration suppresses a leaky wave of a surface acoustic wave in the transversal direction and reduces insertion loss.
However, the acoustic velocity and the insertion loss achieved by the surface acoustic wave device described in Japanese Unexamined Patent Application Publication No. 2008-177885 are not high enough and low enough, respectively.
Leaky elastic waves and Love waves are known as elastic waves that propagate on LiNbO3. Leaky elastic waves have a high acoustic velocity but have a large attenuation constant, which makes it difficult to achieve a low loss. In contrast, Love waves have a low acoustic velocity, which makes it difficult to achieve a high acoustic velocity, but are unlikely to leak.
Therefore, it has been attempted to increase the acoustic velocity by using a leaky elastic wave and by stacking a high acoustic velocity film in the related art. However, since the acoustic velocity is high in a structure in which a high acoustic velocity film is stacked, a leaky elastic wave is output and an attenuation constant undesirably increases.